544 



SCIENTIFIC RECORD FOR 1883. 



the barometer, states that Kamtz had already, in 1834, in his Lehrbuch, 

 graphically presented the lines of equal barometric ranges, a method 

 that has been neglected until in most recent times, when Felberg (1878) 

 and Koppen (1882) have published contributions to this subject not- 

 withstanding the difficulty of obtaining uniform or homogeneous results 

 for many countries. Koppen has been able to make a very extensive 

 collection, fairly representing the whole northern hemisphere, and with 

 numerous points of comparison in the southern hemisphere, from which 

 we extract the following table of mean monthly barometric variability: 



By comparing the figures in this table with values based on dynam- 

 ical formuhe due to Ferrel and Guldberg, Koppen concludes that the 

 great difference between the mean variability over the land and sea is 

 to be referred to the variable influence of the earth's rotation in differ- 

 ent latitudes and the resistances offered by the surface of the earth to 

 the movement of the air. He finds that in winter the quantity of air 

 passing over any latitude in a unit of time is the same in all latitudes, 

 but in summer the quantity is sensibly diminished north of latitude 10°, 

 perhaps because of the greater quantity of vapor and latent heat in the 

 tropics. The hypothesis that the friction increases the barometric 

 variation especially explains the relative variations, which are greater 

 on sea than on land in latitudes between 30° and 70° north, but at the 

 equator are smaller on sea than on land. Finally, the inflow of air at 

 the earth's surface, or the outflow in the outer strata is approximately 

 equal in all latitudes during the winter, but in summer diminishes, first 

 rapidly then slowly for increase in latitudes. The general proportionality 

 of the barometer variations to the mean barometric gradient gives us 

 further corresponding variations with the mean velocity of the wind, &c. 

 (Z. O. G. M., xviii, p. 7.) 



IX. — GENERAL, AND LOCAL STORMS. 



Koppen has published a chart showing the frequency of and princi- 

 pal paths pursued by centers of barometric minima for the region be- 

 tween the Rocky Mountains and the Ural. His charts are based on the 



